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<meta name="description" content="代码块是一个不重要的概念，但是作为结构清楚一下就可以了。所谓的代码块指的是使用了{}定义的一段程序代码，而代码块根据其定义的位置以及声明的关键字的不同，一共可以分为四类：普通代码块，构造块，静态块，同步代码块。 普通代码块普通代码块指的是定义在方法中的代码块。 范例：观察一个简单程序 1234567891011121314package 普通代码块;public class Demo &amp;#123;">
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<meta property="og:description" content="代码块是一个不重要的概念，但是作为结构清楚一下就可以了。所谓的代码块指的是使用了{}定义的一段程序代码，而代码块根据其定义的位置以及声明的关键字的不同，一共可以分为四类：普通代码块，构造块，静态块，同步代码块。 普通代码块普通代码块指的是定义在方法中的代码块。 范例：观察一个简单程序 1234567891011121314package 普通代码块;public class Demo &amp;#123;">
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<meta name="twitter:description" content="代码块是一个不重要的概念，但是作为结构清楚一下就可以了。所谓的代码块指的是使用了{}定义的一段程序代码，而代码块根据其定义的位置以及声明的关键字的不同，一共可以分为四类：普通代码块，构造块，静态块，同步代码块。 普通代码块普通代码块指的是定义在方法中的代码块。 范例：观察一个简单程序 1234567891011121314package 普通代码块;public class Demo &amp;#123;">



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          <h2 class="post-title" itemprop="name headline">Java 代码块</h2>
        

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        <p>代码块是一个不重要的概念，但是作为结构清楚一下就可以了。所谓的代码块指的是使用了<code>{}</code>定义的一段程序代码，而代码块根据其定义的位置以及声明的关键字的不同，一共可以分为四类：普通代码块，构造块，静态块，同步代码块。</p>
<h1 id="普通代码块"><a href="#普通代码块" class="headerlink" title="普通代码块"></a>普通代码块</h1><p>普通代码块指的是定义在方法中的代码块。</p>
<p>范例：观察一个简单程序</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 普通代码块;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        <span class="keyword">if</span>(<span class="keyword">true</span>)&#123;<span class="comment">//表示该判断一定成立</span></span><br><span class="line">            <span class="keyword">int</span> x = <span class="number">10</span>;<span class="comment">//局部</span></span><br><span class="line">            System.out.println(x);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">int</span> x = <span class="number">100</span>;<span class="comment">//全局</span></span><br><span class="line">        System.out.println(x);</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>如果你将if语句拿掉，就将成为普通代码块了。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 普通代码块;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        &#123;<span class="comment">//直接使用大括号进行定义，就是普通代码块</span></span><br><span class="line">            <span class="keyword">int</span> x = <span class="number">10</span>;<span class="comment">//局部</span></span><br><span class="line">            System.out.println(x);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">int</span> x = <span class="number">100</span>;<span class="comment">//全局</span></span><br><span class="line">        System.out.println(x);</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>个人觉得 ：如果你现在的方法中代码写的过长，但是又需要避免变量重名问题，往往会使用普通代码块，但是一般人真不用。</p>
<h1 id="构造块"><a href="#构造块" class="headerlink" title="构造块"></a>构造块</h1><p>构造块指的是定义在类中的代码块。</p>
<p>范例：定义构造块</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 构造快;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    &#123;</span><br><span class="line">        System.out.println(<span class="string">"Person的构造块"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person的构造方法"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>每一次使用关键字new实例化对象的时候一定会调用构造方法，但是有了构造块之后发现构造块会优先于构造方法先执行。这个构造块唯一的好处是可以进行一些简单的逻辑操作，但是又没什么用。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 构造快;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String info = <span class="string">"hello"</span>;</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">int</span> x = <span class="number">0</span>;x &lt; <span class="number">10</span>;x++)&#123;</span><br><span class="line">            info+=x;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person的构造方法"</span>+info);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>构造块的使用只是一种补充手段，而这种手段恰恰没有意义。</p>
<h1 id="静态代码块"><a href="#静态代码块" class="headerlink" title="静态代码块"></a>静态代码块</h1><p>静态代码块指的是使用了static关键字定义的代码块。但是如果要去考虑我们的静态块必须分为两种情况：</p>
<ul>
<li>在非主类中定义的静态块；</li>
<li>在主类中定义的静态块；</li>
</ul>
<p>范例：观察静态块操作</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 静态块;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    &#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的构造块"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的构造方法"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">static</span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的静态块"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>可以发现静态块优先于构造块先执行，而且不管产生多少个实例化对象，静态块也只使用一次。静态块最为主要的作用就是为static属性初始化。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 静态块;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> String info = <span class="string">"hello"</span>;</span><br><span class="line">    &#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的构造块"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的构造方法"</span> + info);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">static</span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的静态块"</span>);</span><br><span class="line">        info +=<span class="string">"world!!"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>静态块也可以定义在主类里面，那么此时的静态块将优先于主方法执行。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> 静态块;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span></span>&#123;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> String info = <span class="string">"hello"</span>;</span><br><span class="line">    &#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的构造块"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Person</span><span class="params">()</span></span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的构造方法"</span> + info);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">static</span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"Person类的静态块"</span>);</span><br><span class="line">        info +=<span class="string">"world!!"</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Demo</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span></span>&#123;</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">        <span class="keyword">new</span> Person();</span><br><span class="line">        System.out.println(<span class="string">"+++++++++++++"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">static</span>&#123;</span><br><span class="line">        System.out.println(<span class="string">"**********"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>一般而言，也没有什么意义了。</p>
<p>如果需要在一些属性使用前做处理就使用构造块或者静态块来完成。</p>

      
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